The invention relates to the general field of GMR read heads for magnetic disk systems with particular reference to use of buried leads and photoresist processes therewith,
Read-write heads for magnetic disk systems have undergone substantial development during the last few years. In particular, older systems in which a single device was used for both reading and writing, have given way to configurations in which the two functions are performed by different structures, The magnetic field that xe2x80x98writesxe2x80x99 a bit at the surface of a recording medium is generated by a flat coil whose magnetic flux is concentrated within two pole pieces that are separated by a small gap (the write gap). Thus, most of the magnetic flux generated by the flat coil passes across this gap with peripheral fields extending out for a short distance where the field is still powerful enough to magnetize a small portion of the recoding medium.
The present invention is concerned with the manufacture of the read element, This is a thin slice of material located between two magnetic shields, one of which is also one of the two pole pieces mentioned above. The principle governing operation of the read sensor is the change of resistivity of certain materials in the presence of a magnetic field (magneto-resistance). In particular, most magnetic materials exhibit anisotropic behavior in that they have a preferred direction along which they are most easily magnetized (known as the easy axis). The magneto-resistance effect manifests itself as a decrease in resistivity when the material is magnetized in a direction perpendicular to the easy axis, said decrease being reduced to zero when magnetization is along the easy axis. Thus, any magnetic field that changes the direction of magnetization in a magneto-resistive material can be detected as a change in resistance.
It is now known that the magneto-resistance effect can be significantly increased by means of a structure known as a spin valve. The resulting increase (known as Giant magneto-resistance or GMR) derives from the fact that electrons in a magnetized solid are subject to significantly less scattering by the lattice when their own magnetization vectors (due to spin) are parallel (as opposed to anti-parallel) to the direction of magnetization of the solid as a whole.
The key elements of a spin valve structure are, in addition to a seed layer and a cap layer, two magnetic layers separated by a non-magnetic layer. The thickness of the non-magnetic layer is chosen so that the magnetic layers are sufficiently far apart for exchange effects to be negligible (the layers do not influence each other""s magnetic behavior at the atomic level) but are close enough to be within the mean free path of conduction electrons in the material. If, now, these two magnetic layers are magnetized in opposite directions and a current is passed through them along the direction of magnetization, half the electrons in each layer will be subject to increased scattering while half will be unaffected (to a first approximation). Furthermore, only the unaffected electrons will have mean free paths long enough for them to have a high probability of crossing the non magnetic layer. However, once these electron xe2x80x98switch sidesxe2x80x99, they are immediately subject to increased scattering, thereby becoming unlikely to return to their original side, the overall result being a significant increase in the resistance of the entire structure.
In order to make use of the GMR effect, the direction of magnetization of one of the layers must be permanently fixed, or pinned. Pinning is achieved by first magnetizing the layer (by depositing and/or annealing it in the presence of a magnetic field) and then permanently maintaining the magnetization by over coating with a layer of antiferromagnetic material. The other layer, by contrast, is a xe2x80x9cfree layerxe2x80x9d whose direction of magnetization can be readily changed by an external field (such as that associated with a bit at the surface of a magnetic disk).
On Feb. 5, 1999, application Ser. No. 09/244,882, entitled xe2x80x9cMagnetoresistive (MR) sensor element with sunken lead structurexe2x80x9d was filed with the US Patent Office. This document discloses the structure shown in FIG. 1, along with a process for manufacturing it. Shown there is a substrate 11 (usually a dielectric material such as aluminum oxide) which has been ion milled to give its central portion the shape of a mesa (shown as 18). On the top of the mesa is seed layer 16 over which GMR sensor 15, a complex of several layers, as discussed above, has been formed. On the area surrounding the mesa 18, conductive leads 12 have been formed. These generally have the shape of a pair of stripes separated by seed layer 16. They may comprise a single material or a laminate of several materials.
Seed layer 13 has been deposited onto the leads 12 and then overcoated with a pair of longitudinal bias stripes 14. The latter are made of a suitable magnetic material and, in the finished device, are permanently magnetized in a direction parallel to the surface of seed layer 16. Their purpose is to prevent the formation of multiple magnetic domains in the free layer portion of the GMR sensor, particularly near its ends.
While the structure shown in FIG. 1 has proven to be an effective package for a GMR sensor and its leads, early versions of said structure were found to exhibit lower than expected GMR ratios. The cause of this problem was found to be the presence of an oxide layer at the interface between layers 15 and 16. The present invention is directed to finding a solution to this problem.
A routine search of the prior art was performed but no references that describe the solution disclosed in the present invention were encountered. Several references of interest were found, however. For example in U.S. Pat. No. 5,985,162, Han et al. show a conductive lead process using a PMGI/PR bilayer structure. Chen et al. (U.S. Pat. No. 5,491,600) and Pinarbasi (U.S. Pat. No. 5,883,764) show other conductive lead processes/etches using a PMGI/PR bilayer structure while Lee et al. (U.S. Pat. No. 5,731,936) show a seed layer for a MR.
It has been an object of the present invention to provide an improved process for the manufacture of a sensing element for a magnetic disk system.
Another object of the invention has been that said sensing element be based on the GMR effect and have buried leads.
A further object has been that said process include a photoresist liftoff step.
These objects have been achieved by including in the process deposition of a protective layer over the seed layer on which the spin valve structure will be grown. This protective layer remains in place while buried leads and longitudinal bias means are formed, including use of a photoresist liftoff process. It is removed as a natural byproduct of surface cleanup just prior the formation of the spin valve.